Mass 6.00 g of a certain compound X, known to be made of carbon, hydrogen and perhaps oxygen, and to have a molecular molar mass of 180. g/mol, is burned
completely in excess oxygen, and the mass of the products carefully measured:
product
carbon dioxide 8.80 g
3.60 g
Use this information to find the molecular formula of X.
water
alo
O
х
?

The molecular formula =C₆H₁₂O₆

Given

6.00 g of a certain compound X

The molecular molar mass of 180. g/mol

CO₂=8.8 g

H₂O=3.6 g

Required

The molecular formula

Solution

mass C in CO₂ :

= 1.12/44 x 8.8

= 2.4 g

mass H in H₂O :

= 2.1/18 x 3.6

= 0.4 g

Mass O in compound :

= 6-(2.4+0.4)

= 3.2 g

Mol ratio C : H : O

= 2.4/12 : 0.4/1 : 3.2/16

= 0.2 : 0.4 : 0.2

= 1 : 2 : 1

The empirical formula : CH₂O

(CH₂O)n=180 g/mol

(12+2+16)n=180

(30)n=180

n=6

(CH₂O)₆=C₆H₁₂O₆